| 1. |
- Andreas, Lale, et al.
(författare)
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Use of secondary materials in landfill constructions
- 2007
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Ingår i: SARDINIA 2007. - Cagliari : CISA, Environmental Sanitary Engineering Centre. - 9788862650038
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Konferensbidrag (refereegranskat)abstract
- Many landfills are subject to closure in the near future. Roughly 2,000 hectares of landfill area have to be covered only in Sweden, equivalent to about 100 million tonnes of construction material. In addition to material costs in the order of tens of billions Euro, this also puts a strain on the environment through the exploitation of non-renewable virgin construction materials. Many landfill operators are considering alternative cover designs and materials in order to reduce resource spending. However, there is a fair amount of uncertainty with regard to functional and environmental consequences of using alternative (secondary) materials, both from the side of the companies and the authorities. This paper gives an overview over potential waste based construction materials and the use of some of them in projects presently ongoing in Sweden.Research on the use of secondary materials in landfill covers is quite recent. Substitutes for natural or synthetic materials in a landfill cover can be various types of waste from process industry, construction and demolition, or comparable activities. Alternative materials that have been investigated are ashes, slags, sewage and fibre sludges, treated soils and compost. Table 1 gives an overview over potential waste based construction materials. The total of potential materials is well in excess of the material needs for landfill construction, but they may not be available at the right time, place or quality.Besides being economically viable, the substitute materials should have suitable technical and environmental properties in order to secure a proper function of the construction. Experiences from three field studies (landfills at Tveta/Södertälje, Hagfors and Alvkarleby) are discussed looking at relevant issues during 1) construction, 2) active after care phase, and 3) long term processes.Using SCM poses additional problems compared to using conventional materials. Often, the supply of material has to be planned in advance and the materials may have to be stored on site. Storing, however, can cause problems if the materials have properties that change over time e.g. due to climate. For other materials storing may be necessary in order to achieve desired properties. One example is the ageing of strongly alkaline materials that react with atmospheric carbon dioxide and thus obtain better leaching properties. Table 1 Overview over potential waste based construction materials and examplesSourceExamplesMining and mineral industryWaste rock, flotation sand, etc...Construction and demolition (C&D)Crushed concrete, gypsum, asphalt, reinforced polymers, woodProcess industryDifferent types of slag from steel making, green liquor and fibre sludge from paper production, ashes and foundry wastesWastewater treatmentDigested sewage sludge, sandIncinerationBottom ash, fly ashThe evidence is mounting that the desired technical function of a landfill cover can be attained using suitable combinations of secondary construction materials. So far, all three field tests indicate leachate amounts between less then one and 30 l (m2 yr)-1 below the liner. In comparison with the average annual precipitation of about 600 mm yr-1 at the Swedish East coast, only 0.2-5 % of the precipitation seeped through the liner so far; i.e. the leachate generation is reduced with about 90 % or more.The issue is more if the materials may cause adverse impacts of the landfill and its recipients. A low water infiltration through the liner means that the most of infiltrating water is removed as drainage water and thus the leaching of the layers above the liner are of the greatest concern.Infiltrating water will yield a liquid to solid ratio of about 1-2 l kg-1 in the layers above the liner after about 10 years. The most mobile elements, such as nitrogen, will be leached to a great extent already at such low L/S ratios, so a forecast with regard to the need of treatment of drainage water points at about two to three decades.In the long term perspective the mineral changes of the construction materials become important. E.g. one of the incentives for using fly ash in liners is their capacity for chemical-mineralogical changes leading to the formation of clay-like structures. This could mean that a liner built of ashes will attain a lower permeability over time. Other mineral changes that can occur in ashes include the trapping of metals in the structure, e g in clay and carbonate phases.Much is still to be learned about the long term processes and the factors that control them. Ongoing studies include the assessment of climatic variables, different material combinations as well as the impact of landfill gases.The following conclusions can be drawn:The use of secondary materials in construction is important due to substantial resource and environmental impacts. An increased use should be beneficial, provided that the problems of using such materials can be managed.In addition to legislative and bureaucratic barriers, there are also practical issues which need to be dealt with in order to pave the way for a wider use of alternative construction materials. In the construction phase more planning is needed due to temporal and geographical limitation of the material availability. Some materials are not ready for immediate use but need to be pre-treated. All of these factors may cause a need for more space and time. A system for quality assurance comparable to that of traditional construction materials is another issue that needs to be resolved. Most likely some kind of legislative pressure is needed for this.In the medium term leaching of pollutants from the construction materials may be the most important issue when using secondary construction materials, which underlines the double standards applied, since traditional construction materials will not be scrutinized in the same manner. Anyhow, the long term interactions between materials and their environment need to be considered and further studies are necessary for secondary construction materials as well as for conventional materials. Existing data indicate both possibilities and problems.In the long term issues of material interactions will remain and the mechanical impact of mineral changes in the secondary construction materials may be added to the list of issues to clarify. Some of the material changes may be beneficial for the function of the construction, e.g. clay formation in liner materials may make them more impervious, but there may also be negative changes caused by deteriorated material properties. The rate and extent of such processes and the factors that enhance or retard them need to be understood better.Secondary construction materials have always been used and some of the "traditional" materials used today were wastes before. There is no reason to believe that this development should not continue.
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| 2. |
- Dahlén, Lisa, et al.
(författare)
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Comparison of total waste flow from households in 35 Swedish municipalities
- 2007
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Ingår i: SARDINIA 2007. - Cagliari : CISA, Environmental Sanitary Engineering Centre. - 9788862650038
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Konferensbidrag (refereegranskat)abstract
- The objective of the study was to identify the total waste flow from households in a number of municipalities (cities) in Sweden, make comparisons and discuss methods as well as obstacles to benchmarking. Overall aim is decision support for local authorities in waste management planning. Average amount of household waste per citizen vary widely within Sweden. There is no obvious explanation to the inconsistent amounts. Weight based collection fees has caused a considerable decrease of collected waste amounts in some Swedish municipalities, but no clear effect in others. In general the amounts per capita of separated recyclables, as well as unseparated waste in bins and bags, have levelled out the last few years. In contrast the diverse wastes delivered by the public to supervised Recycling Centers show a trend of increase. 16 sources of error in collection data have been identified and described.
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| 3. |
- Diener, Silvia, et al.
(författare)
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Mineral transformations in steel slag used as landfill cover liner material
- 2007
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Ingår i: SARDINIA 2007. - Cagliari : CISA, Environmental Sanitary Engineering Centre. - 9788862650038
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Konferensbidrag (refereegranskat)abstract
- In Europe, 15.2 million tonnes of steel slags have been generated in 2004 (Euroslag, 2006) out if which almost 6 million tonnes came from electric arc furnace (EAF) steelmaking and secondary metallurgical processes. In the presented project from Luleå University of Technology, two types of EAF slag and one slag originating from secondary metallurgical processes named ladle slag are investigated. The chemical and physical properties of these slags have been studied in detail (Herrmann, 2006; Andreas et al., 2005). For utilising steel slags in the liner of a landfill cover the long-term stability of the minerals is of great importance. Therefore, the ageing of steel slag minerals is evaluated with the help of a laboratory experiment. Particularly, the research questions, the experimental set-up and the methodology are presented. The present paper is part of a research project of the Division of Waste Science and Technology at Luleå University of Technology, Sweden in cooperation with Uddeholm Tooling AB, Hagfors municipality and MiMeR (Mineral and Metal Recycling Research Centre). It is investigated if steel slags are stable as a landfill cover liner material. The long-term stability is evaluated by determining the factors influencing the mineralogy of the slags and possible mineral transformations through ageing under the environmental conditions in a liner. The experiment includes two similar types of EAF slag and one ladle slag. Each steel slag sample is made by mixing 50% EAF slag and 50% ladle slag, addition of water and compaction. The specimens are stored in boxes under different atmospheric conditions. A reduced multivariate design has been chosen to determine the impact of different factors on the slag mineralogy. The factors that are varied in the experiment are relative humidity, carbon dioxide and temperature of the atmosphere surrounding the slag material as well as ageing time and the quality of the water used for sample making (see table 1). Table 1. Factorial design for ageing experiment of steel slagsLowMiddleHighRelative humidity30% -100%Carbon dioxide content0.036 (air)20 % * 100 %Temperature5 °C30 °C60 °CTime 1 month6 months1 yearWater quality destilled water -LeachateThe ageing of minerals is expected to initiate mineral transformations in steel slags. Primary phases will alter into secondary mineral phases. Changes in mineralogy can influence the stability of the liner. To evaluate mineralogy and properties of the aged steel slag, different analyses will be performed after the storage time of the specimens. X-ray diffraction and scanning electron microscopy as well as shear strength, acid neutralisation capacity and cation exchange capacity will be included. A possible mineral transformation for an alkaline material as steel slags can be the reaction of calcium ions from calcium silicates with the carbon dioxide resulting in the precipitation of calcium carbonate. Through this carbonation reaction, the transport of carbon dioxide into the bulk of the specimen could be hindered by the reaction products. Therefore, surface morphology can influence mineral transformations. First results and evaluations will be presented at the conference. REFERENCES Andreas L., Herrmann I., Lidstrom-Larsson M. & Lagerkvist A. (2005) Physical properties of steel slag to be reused in a landfill cover, Sardinia 2005, Tenth International Waste Management and Landfill Symposium, S. Margherita di Pula, Cagliari, Italy; 3 - 7 October 2005Euroslag (2006) Legal status of Slags. Position Paper. January 2006. The European Slag Association - EUROSLAG. Duisburg, Germany.Herrmann I. (2006). Use of Secondary Construction Material in Landfill Cover Liners. Licentiate Thesis. Luleå University of Technology, Sweden.
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| 4. |
- Travar, Igor, et al.
(författare)
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Environmental impact of ashes used in a landfill cover construction
- 2007
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Ingår i: SARDINIA 2007. - Cagliari : CISA, Environmental Sanitary Engineering Centre. - 9788862650038
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Konferensbidrag (refereegranskat)abstract
- Large amounts of construction materials will be needed both in Sweden and other European countries for capping landfills that will be closed in the near future. In order to reduce exploitation of virgin materials and to save natural resources, an option can be utilization of various types of secondary construction materials (SCM) e.g. ash, slag, sand from fluid bed incineration and compost. However, at the same time this may represent potential risks due to the release of trace elements and other pollutants into environment. The main aim of this work is to evaluate the environmental impact of water that discharges from different parts of a landfill cover built with ashes and other SCM.From 2003 to 2005, a four hectares large test area was established at Tveta landfill, southwest of Stockholm, Sweden. Test area is divided into six sub areas with regard to different recycled materials used in different layers of the cover construction (Figure 1).Figure 1. Design of the landfill cover test area at the Tveta landfill. BA = Bottom ash; FA = Fly ash; FC = Friedland clay Infiltrating water through the landfill cover either drains off in the drainage layer as drainage water or percolates through the liner into landfill body as leachate. At Tveta landfill, leachate amounts between 1 l (m2 yr)-1 and 30 l (m2 yr)-1 have been observed below highly compacted ash liner. Results show that leachate samples have higher pH, salt forming elements (e.g. K, Na, Ca and Cl) and concentrations of Cd, Ba As, Al, and Mo, and lower concentrations of Mn, Zn, Mg, Fe, Ni, and Pb compared to drainage water. The concentrations of Cr and total N are in the same range in leachate and drainage water while NH4-N is higher in leachate. Leachate of areas 1 and 4 shows higher content of organic matter than drainage water in these areas. A strong correlation is observed between EC, K, Na and Cl as well as between Cu and TOC. The comparison of the leachate and drainage water quality with different limit values showed that the leachate had elevated concentrations of As, Mo, Cl and nitrogen while the drainage water was mainly contaminated by Ni, Zn, Cl and nitrogen with the addition of As, Cu, Mo, and Pb in areas 2 and 4.Following conclusions can be drawn by now:The hydraulic properties of the landfill cover satisfy legislative requirements for non hazardous waste landfills; in some cases/areas also for hazardous waste landfills.Most of the infiltrating water through the landfill cover is discharged as drainage water. Thus, the design of layers above the liner is most important with regard to the environmental impact of the construction. Both leachate and drainage water need treatment before discharge into the local recipient. Organic matter in the protection layer is likely to contribute to the mobilization of Cu and Ni in short term.The sea might be a suitable recipient in cases where ashes are used in landfill covers because both leachate and drainage contain salt forming elements in elevated concentrations which may harm groundwater or freshwater but do not pose a risk to salt-water.The leaching of most pollutants did not show any clear tendencies during first three years. Thus, assessing the time period for treatment needs is difficult. However, it is expected that the contaminants in the drainage water will be depleted within few decades.Leachate might be contaminated by salt forming and trace elements for one hundred years. However, generated leachate amounts are low and it is expected that leachate from landfill cover will not influence overall landfill leachate with full extent.The ageing of the ashes in connection with mineral transformations is an important process that is expected to reduce the release of pollutants. Further research is needed with regard to long term changes of the material properties and the treatment needs for water.
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